We propose the use of an intercross-backcross breeding protocol with selective genotyping to identify, map, and characterize the genes responsible for the high alcohol preference trait expressed by C57BL/6 mice. In our studies to date, we have identified and localized a previously-unpredicted alcohol preference locus - Alcp1 - at a high level of significance (P <0.00018) to an 8 cM interval on one mouse chromosome. A second alcohol preference locus - Alcp2 - has been tentatively localized on a second chromosome (P <0.0013). Both of these loci map close to genes involved in serotonin activity. The specific aims of this research proposal are: 1. Identification of loci involved in the alcohol preference trait expressed by B6 mice. Additional offspring from the (B6 X DBA) X B6 backcross will be screened to obtain a total set of 300 animals that express the high alcohol preference trait. A stratified analysis of these animals with sets of microsatellite markers will allow us to identify and map QTLs showing an association of at least 6O% with the alcohol preferring class. Correlations among multiple QTLs will be defined and used to evaluate various models of genetic interactions. A second backcross will be analyzed to assess the generality of the results obtained with B6 and DBA. 2. Genetic and molecular analysis of candidate alcohol preference genes. Candidate serotonin-related genes already identified, and any others suggested by the mapping studies of specific aim 1, will be tested for co-segregation with Alcp1, Alcp2 , or further Alcp loci that are uncovered. Candidate genes that survive this genetic test will be assayed for coding sequence and RNA transcriptional differences between parental B6 and DBA alleles. 3. Further neurochemical and behavioral studies of alcohol-preferring mice. In collaboration with Professor Bart Hoebel, alcohol-preferring mice will be analyzed for the expression of additional addictive behavior traits and for specific neurochemicals predicted to play a role in these traits based on the genetic results of aims 1 and 2. If additional associations of any kind are observed, the accumulated data will be used to determine the specificity of genotype-phenotype relationships.